Quantifying Heat Flow Chemical Change UNIT 4 Day 4 What are we - - PowerPoint PPT Presentation

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Quantifying Heat Flow Chemical Change UNIT 4 Day 4 What are we - - PowerPoint PPT Presentation

Nov 29, 2023 103 likes •246 views

Sparks CH301 THERMODYNAMICS Quantifying Heat Flow Chemical Change UNIT 4 Day 4 What are we going to learn today? Use calorimetry to calculate H rxn Use different methods to calculate H rxn Define Heats of Formation, Hesss Law, and

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Sparks CH301 THERMODYNAMICS Quantifying Heat Flow – Chemical Change UNIT 4 Day 4

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SLIDE 2

What are we going to learn today?

Use calorimetry to calculate ΔHrxn Use different methods to calculate ΔHrxn Define Heats of Formation, Hess’s Law, and Bond Energies

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A bomb calorimeter measures heat at constant volume, which is equivalent to a) ΔU b) ΔH c) Work

QUIZ: iClicker Question

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Calorimetry Example

  • To perform the following reaction, we add

0.10 mole of ICl to a bomb calorimeter whose heat capacity is 1.14 kJ/oC. The temperature

  • f 5000 g of water rose from 25.00oC to

25.081oC. Determine ∆E for the reaction in kJ/mol. ICl(g)  ½ I2(s) + ½ Cl2(g)

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DH and DE Example

  • An exothermic reaction was carried out in a

constant pressure calorimeter. 75 kJ of heat was given off and the expanding gases pushed back on the surrounding atmosphere doing 10kJ of work. What are DH and DE?

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Calculating both ∆H and ∆E, a simple review

  • At 25ºC and 1.0 atm, 2 mol sulfur dixoide

reacts with oxygen to give sulfur trioxide: 2 SO2(g) + O2(g)  2 SO3(g) The reaction releases 200 kJ as heat. Calculate ∆H and ∆E for this process.

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Example: Getting Thermochemical Equation (Reaction Enthalpy) from Bomb Calorimetry Data

  • 1.56 g of benzene, C6H6, was burned in a

constant volume (bomb) calorimeter, liberating 65.25 kJ of heat.

  • A. Write the standard chemical equation for this

reaction for 1 mole of the fuel.

  • B. Calculate ΔE in kJ/mol.
  • C. Calculate ΔHcombustion for benzene in kJ/mol.
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Compare these two problems

The one we just worked: 1.56 g of benzene, C6H6, was burned in a constant volume (bomb) calorimeter, liberating 65.25 kJ of heat.

  • C. Calculate ΔHcombustion for

benzene in kJ/mol. This one: Using a bomb calorimeter

  • f heat capacity 155

J/oC, containing 1000 ml

  • f water, 1.56 g of

benzene was burned. The temperature of the water went from 23oC to

  • 38oC. Use this data to

find DHcombustion for benzene.

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Compare these two problems

The one we just worked: 1.56 g of benzene, C6H6, was burned in a constant volume (bomb) calorimeter, liberating 65.25 kJ of heat.

  • C. Calculate ΔHcombustion for

benzene in kJ/mol. This one: Using a bomb calorimeter

  • f heat capacity 155

J/oC, containing 1000 ml

  • f water, 1.56 g of

benzene was burned. The temperature of the water went from 23oC to

  • 38oC. Use this data to

find DHcombustion for benzene.

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SLIDE 10
  • Internal E and

Enthalpy

– ΔE = q + w – The relationship between ΔE and ΔH – Determining enthalpy experimentally: calorimetry – Determining ΔH from tabulated data

  • Entropy!

What we’ve learned so far: Our next topics:

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The transfer of heat energy into or out of a system at constant pressure is a state function called Enthalpy. The change in Enthalpy can be determined experimentally using a coffee cup calorimeter at constant pressure. The change in Enthalpy can be calculated based on a variety

  • f tabulated data:

Heats of formation/Other Heats of Reaction/Bond Energies

What have we learned today?

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Write a formation chemical equation for a compound Calculate change in enthalpy for a reaction based on calorimetry data Calculate change in enthalpy for a reaction based on tabulated data (Hess’s law, formation data, bond energy data).

Learning Outcomes

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Important Information

HW